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Abstract

The intrinsic photo-response of chemical vapor deposited (CVD) graphene photodetectors were investigated after eliminating the influence of photodesorption using an atomic layer deposited (ALD) Al2O3 passivation layer. A general model describing the intrinsic photocurrent generation in a graphene is developed using the relationship between the device dimensions and the level of intrinsic photocurrent under UV illumination.

Figures (4)

Fig. 1 (a) Top-down SEM image of a graphene photodetector. (b) Raman spectra of the graphene channel. The inset is a SEM image of the graphene channel that magnifies the white circle in (a). (c) The DC Id-Vg curve of graphene photodetector before the passivation. The graphene channel is exposed to air ambient. (d) The DC Id-Vg curve of the graphene photodetector after the passivation and 200 °C PDA. The graphene channel is passivated with Al2O3.

Fig. 2 Photo-response of (a) an air-exposed graphene photodetector and (b) a Al2O3-passivated graphene photodetector with a UV on/off cycle of 20 seconds (200 μW/cm2 power and 365 nm wavelength UV lamp was used and the graphene photodetectors were biased with Vd = 10 mV and Vg = 0 V).

Fig. 3 Band profile of the graphene photodetector (a) exposed to air ambient without illumination, (b) exposed to air ambient under illumination and (c) after Al2O3 passivation under illumination. ΔΦ (ΔE) denotes the Fermi level shift of graphene due to metal-induced doping (external doping). Shaded area adjacent to the electrode is the transition region (LTS, LTD), black (open) circle denotes electron (hole), arrow denotes the direction in which the carrier is moving, and IPD→ (IPS→) means the direction of the drain (source) side photocurrent. (d) The photocurrent of Al2O3 passivated graphene photodetector measured while modulating the back gate bias with 100 mV of drain bias. (e) Schematic illustration of carrier generation and recombination, photodesorption and re-adsorption of an air-exposed area and Al2O3 passivated area of graphene photodetector under illumination. Red (blue) circle denotes electron (hole). Only photo generated carriers within the drift distance from the electrode can contribute to the photocurrent. UV-induced photodesorption occurred at the air-exposed graphene photodetector resulting hole extraction from the graphene.

Fig. 4 (a) Variation in photocurrent generation as a function of the illumination intensity. (b) 1Hz and 20-second on/off characteristics of graphene photodetectors. The inset is on/off characteristics at 1Hz that magnifies the red rectangle in (b). (c) Photocurrent generation in an Al2O3 passivated graphene measured at different channel width, (d) Photocurrent generation in an Al2O3 passivated graphene measured at different length. Power = 200 μW/cm2, wavelength = 365nm, and Vd = 100 mV were used at for (c) and (d) measurement.